Field of the Disclosure
This application relates a system and a method for control of a twin-tiltrotor helicopter. The twin-tiltrotor helicopter (TTH) is lifted and propelled by two rotors. Twin-tiltrotor helicopters are classified as a rotocraft, as opposed to a fixed-wing aircraft, since the twin-tiltrotor helicopters derive lift from the rotation of revolving airfoils.
Description of the Related Art
In conventional helicopters, the rotational speed of the main rotor is usually kept constant, while control of the helicopters' motion is achieved by altering the pitch of the blades. This position dependent pitch is referred to as ‘cyclic’ and the blade's pitch is based on the blade's position in the rotor disk. However, unlike a conventional helicopter, a multirotor helicopter employs fixed-pitch blades.
The control of a multirotor helicopter is achieved by varying the rotational speed of one or more rotors, thereby changing a torque load, thrust, and lift characteristics of the multirotor helicopter. By comparison, the drag on the blades of the main rotor in conventional helicopters cause the main body of the helicopter to rotate and a rear tail rotor is needed as a balancing moment to counter the drag-induced torque. However, the rear tail rotor of helicopters reduces flight efficiency and does not contribute to the lift force. The multirotor configuration eliminates the need for a rear tail rotor by employing counter-rotation of rotor pairs.
Multirotor helicopters also have additional advantages over conventional helicopters in that multirotor helicopter rotors do not require mechanical linkages to vary the rotor blade pitch angle as the rotor blade spins. This simplifies the design and maintenance of the multirotor helicopter.
More recently, the multirotor helicopter has become popular in unmanned aerial vehicle (UAV) research. These vehicles in related art may use electronic control systems and electronic sensors to help stabilize the aircraft. The multirotor helicopter may be sized compactly for agile maneuverability and can be flown both indoors and outdoors. The multirotor helicopter may be used as a UAV for surveillance and reconnaissance by military and law enforcement agencies, as well as for search and rescue missions in a wide array of environments and conditions, from urban to remote locations. The multirotor helicopter UAVs can be suitable for these tasks due to their autonomous capabilities and cost savings over other conventional methods.
The multirotor helicopters may also be employed in manned aerial vehicles and can be employed in a wide range of commercial and military applications. Such applications may include: heavy transportation, construction of bridges and buildings, assembly of large pieces in factories, and rescue operations after natural disasters where roads and bridges are no longer usable.
For military applications, the multirotor helicopter may perform vertical takeoff and landing (VTOL) and can be used in manned operations for effective transport and for military deployment operations in hostile environments where VTOL is a requirement. Additionally, the multirotor helicopter can have maneuverability that may be superior to helicopters, such as the APACHE helicopter.
The multirotor helicopter structure and control in the related art lacks the flexibility to meet the maneuverability and precision requirements needed for control and air vehicle management of manned multirotor helicopter rotors. Further, multirotor helicopters can be heavy leading to a sluggish or delayed response to a flight command and may require powerful motors to compensate for the rotor weight and slow flight dynamics. There remains a need for an improved, faster and lighter helicopter system and method to provide superior control and precision.